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MEMORANDUM a4 ~Y TO: Bruce Humphries ~~ FR: Harry Posey RE: Sediment to Rito Seco; your 28 August memo What the Board observed on its trip down the Rito Seco and elsewise during the Battle Mountain tour were, in my judgement, abberations from the norm. What I noticed at the beginning of the day, upon entering the near boundaries of the property, was the incredibly high amount of sediment compared with past trips to the site, in the beaver ponds. It was clear to me that the area had received an unusual rain, relative to all other trips. What I observed at the end of the day was that the ponds were still murky, even thot.gh the flowing part of the stream, above the mine road, was quite clear. As regards the failure of sediment control structures in the ditches leading From the West Pit and access road into the Rito Seco, Larry, Berhan, and I have examined the sediment control structures during various field inspections since April 1, and none cf us ever took note of the perceived need to key in the hay bales, as you mentioned. It is dear that, had the hay bales not failed, there would have been less sediment in the Rito Seco. However, in my observations, these were the only sediment control structures on the mine site that failed. In addition, the overwhelming percentage of sediment coming into the Rito Seco below the mine is from the County Road, and from several large dry washes that feed under the County Road from the north. Someone on the trip (I don't recall who) suggested that the Beaver Dam;. are silting in because of sediment from the mine. Others suggested that they are silting in because of sediment contributions from the County Road and the dry washes from the north. However, I take issue with both of these opinions. The Beaver ponds are silting in because they are Beaver ponds. Period. Beaver ponds all over the world, like any water body behind a dam, silt in eventually because dams slow down the flow and dissapate the streams' energy. A streams ability to carry a sediment load depends on the rate of flow and tt.e sediment to fluid ratio. With any loss of energy, a stream's ability to carry sediment diminishes, and the suspended load begins falling out of suspension. Someone else suggested, perhaps carelessly, that the beaver dams should t>e removed in order to stop siltation. This idea is exactly bacllvard, and very wrong-headed. If the Beaver dams are taken out, most of the silt behind the dams will find its way into future storm water, and the silt will be carried out into the valley. Regarding Mr. Jaquez' attempts to measure the effects of the mine on siltation to the Ri[o Seco, I note several oversights. Not only are his two sampling points located in two very different fluvial regimes, they are also located in two extremely different vege~.ation regimes, and two different bedrock/sediment regimes. The upstream sampling point is located at a